Date:	Fri, 07 Jan 2011 15:43:01 -0500
From:	Chase Douglas <chase.douglas@...onical.com>
To:	Henrik Rydberg <rydberg@...omail.se>
CC:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Chris Bagwell <chris@...bagwell.com>,
	Peter Hutterer <peter.hutterer@...-t.net>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] Documentation: Add evdev type and code definitions

On 12/16/2010 09:12 AM, Henrik Rydberg wrote:
> On 12/14/2010 10:21 PM, Chase Douglas wrote:
>> +The evdev protocol uses a map of types and codes to express input device values
>> +to userspace. This document describes the types and codes and how and when they
>> +may be used.
> 
> 
> On a general note, the transfer is stateful. It is assumed that the receiver
> knows that prior state of an axes when the new value comes in. Only changed
> values are emitted.
> 
> Most of the input state can be retrieved via ioctl/sysfs calls.

I've noted both of these for the next revision.

>> +* SYN_REPORT:
>> +  - Used to synchronize and separate events in time. For example, motion of a
>> +    mouse may set the REL_X and REL_Y values for one motion, then emit a
>> +    SYN_REPORT. The next motion will emit more REL_X and REL_Y values and send
>> +    another SYN_REPORT.
> 
> 
> We have not using the name @frame@ much so far, but i think it is a good name
> for it.

Good idea. I began using 'frame' name for the next revision.

>> +* BTN_TOOL_<name>, BTN_TOUCH:
>> +  - These codes are used in conjunction with input trackpads, tablets, and
>> +    touchscreens. These devices may be used with fingers, pens, or other tools.
>> +    When an event occurs and a tool is used, the corresponding BTN_TOOL_<name>
>> +    code should be set to a value of 1. When the tool is no longer interacting
>> +    with the input device, the BTN_TOOL_<name> code should be reset to 0. All
>> +    trackpads, tablets, and touchscreens should use at least one BTN_TOOL_<name>
>> +    code when events are generated. For non-tablet devices, the tool is usually
>> +    BTN_TOUCH.
> 
> 
> BTN_TOUCH is always required, and on top of that, one or several other BTN_TOOL
> can be used. There is also a quirk in that BTN_TOUCH should come first in the
> event stream, for the benefit of the mousedev emulation driver.

I've tried to address both issues in the next revision.

>> +* BTN_TOOL_FINGER, BTN_TOOL_DOUBLETAP, BTN_TOOL_TRIPLETAP, BTN_TOOL_QUADTAP:
>> +  - These codes denote one, two, three, and four finger interaction on a
>> +    trackpad or touchscreen. For example, if the user uses two fingers and moves
>> +    them on the touchpad in an effort to scroll content on screen,
>> +    BTN_TOOL_DOUBLETAP should be set to value 1 for the duration of the motion.
>> +    Note that these codes and the BTN_TOOL_<name> and BTN_TOUCH codes are
>> +    orthogonal in purpose. A trackpad event generated by finger touches should
>> +    generate events for one code from each group.
> 
> 
> In the input-mt interface, there is a function to report these,
> input_mt_report_finger_count().

I've added a note about this.

>> +* ABS_DISTANCE:
>> +  - Used to describe the distance of a tool from an interaction surface. This
>> +    should only be used while the tool is in close proximity of the device. If
>> +    the input device may be used freely in three dimensions, consider ABS_Z
>> +    instead.
> 
> 
> The word "hovering" is commonly used to describe this usage. Many pen tablets
> use it, and touch versions are emerging.

I added use of the word 'hovering' to be clear.

Thanks!

-- Chase
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